caomaomao1979
幼苗
共回答了19个问题采纳率:84.2% 举报
已知函数
![](https://img.yulucn.com/upload/f/b1/fb18f70cb3b6886fa2c63fa93b833966_thumb.jpg)
,
(Ⅰ)当a=4时,求函数f(x)的单调区间;
(Ⅱ)求函数g(x)在区间
![](https://img.yulucn.com/upload/0/82/082f50cea231b8cf1ce4d0d835c8254c_thumb.jpg)
上的最小值;
(Ⅲ)若存在
![](https://img.yulucn.com/upload/5/99/5991b868f1512706834621515d43b52c_thumb.jpg)
,使方程
![](https://img.yulucn.com/upload/c/0c/c0c00946c8aeb92b238039b5ee767c97_thumb.jpg)
成立,求实数a的取值范围(其中e=2.71828是自然对数的底数)
(Ⅰ)
![](https://img.yulucn.com/upload/6/17/617d35cc647105bf2d64799fff966bed_thumb.jpg)
时,
![](https://img.yulucn.com/upload/9/f9/9f9ec95d1cf060beb71f0e48b2928528_thumb.jpg)
的单调增区间为
![](https://img.yulucn.com/upload/d/ee/dee9b068254de511c20b5a4e24c79331_thumb.jpg)
,单调减区间为
![](https://img.yulucn.com/upload/a/36/a366731f0d38181b41247368b0ce67fb_thumb.jpg)
.
(Ⅱ)
![](https://img.yulucn.com/upload/7/4e/74e2d11121b85e130a38bd586fa73af8_thumb.jpg)
;(III)实数
![](https://img.yulucn.com/upload/7/69/7691011eea27a0df77fcb30ecb93ca53_thumb.jpg)
的取值范围为
![](https://img.yulucn.com/upload/f/77/f77caca4edcb7cd4f1a0cd751d4135f4_thumb.jpg)
.
试题分析:(Ⅰ)求导数,根据
![](https://img.yulucn.com/upload/7/4e/74e007ad984d970df06ce7eb3b15c1fe_thumb.jpg)
,
![](https://img.yulucn.com/upload/8/d9/8d950390f87f13867091624f47cd0cc0_thumb.jpg)
得到函数的单调区间.
(Ⅱ)遵循“求导数,求驻点,讨论单调性,确定最值”.
(III) 由
![](https://img.yulucn.com/upload/f/e9/fe9b99692e28a6a20e8a3fbaab3549e2_thumb.jpg)
可得
“分离参数”得
![](https://img.yulucn.com/upload/1/ec/1ecae08517ce1d671659926b8c3146fd_thumb.jpg)
.
令
![](https://img.yulucn.com/upload/e/6e/e6ea69c0314bb52a6bf3a872aee88059_thumb.jpg)
,遵循“求导数,求驻点,讨论单调性,确定最值”.
“表解法”往往直观易懂,避免出错.
试题解析:(Ⅰ)
![](https://img.yulucn.com/upload/8/2f/82fcf08116d1ba64d882dcb6970ea429_thumb.jpg)
1分
当
![](https://img.yulucn.com/upload/6/17/617d35cc647105bf2d64799fff966bed_thumb.jpg)
时,
![](https://img.yulucn.com/upload/2/e0/2e01aaa87a6ea2f45cc843c40aefac2a_thumb.jpg)
,令
![](https://img.yulucn.com/upload/7/4e/74e007ad984d970df06ce7eb3b15c1fe_thumb.jpg)
得
![](https://img.yulucn.com/upload/b/ba/bba702d97a123bcc2cc0b2b30b25e6ec_thumb.jpg)
2分
∴当
![](https://img.yulucn.com/upload/6/17/617d35cc647105bf2d64799fff966bed_thumb.jpg)
时,
![](https://img.yulucn.com/upload/9/f9/9f9ec95d1cf060beb71f0e48b2928528_thumb.jpg)
的单调增区间为
![](https://img.yulucn.com/upload/d/ee/dee9b068254de511c20b5a4e24c79331_thumb.jpg)
,单调减区间为
![](https://img.yulucn.com/upload/a/36/a366731f0d38181b41247368b0ce67fb_thumb.jpg)
. 3分
(Ⅱ)
![](https://img.yulucn.com/upload/3/9e/39e6ca836105fdd376d0266edaddf0ce_thumb.jpg)
, 令
![](https://img.yulucn.com/upload/b/6e/b6ee6f0b48549c78a07564163dd4c9da_thumb.jpg)
,得
![](https://img.yulucn.com/upload/e/23/e2303e61f67f3c1b4fd307a666f8a732_thumb.jpg)
4分
①当
![](https://img.yulucn.com/upload/4/f1/4f17c474bae0eb7a7191a4fe428d8f9d_thumb.jpg)
时,在区间
![](https://img.yulucn.com/upload/3/d9/3d9e5061f51b1efc4e47f0b33a00b558_thumb.jpg)
上
![](https://img.yulucn.com/upload/b/6e/b6ee6f0b48549c78a07564163dd4c9da_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/49/449c290e48409d553cc1cda953f02466_thumb.jpg)
为增函数,
∴
![](https://img.yulucn.com/upload/5/47/5473ea5f06e92adb33926ab6b1ebc00d_thumb.jpg)
5分
②当
![](https://img.yulucn.com/upload/4/04/404272a54109d15b34c543a9acb055e4_thumb.jpg)
时,在区间
![](https://img.yulucn.com/upload/3/21/3214449997a63dd1a0f21b3bfef5b619_thumb.jpg)
上
![](https://img.yulucn.com/upload/6/cf/6cfbee50d245fcc81989306ac0f80b15_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/49/449c290e48409d553cc1cda953f02466_thumb.jpg)
为减函数, 6分
在区间
![](https://img.yulucn.com/upload/8/d1/8d18ab35e6814bc3f38119f88c185ccf_thumb.jpg)
上
![](https://img.yulucn.com/upload/b/6e/b6ee6f0b48549c78a07564163dd4c9da_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/49/449c290e48409d553cc1cda953f02466_thumb.jpg)
为增函数, 7分
∴
![](https://img.yulucn.com/upload/7/4e/74e2d11121b85e130a38bd586fa73af8_thumb.jpg)
8分
(III) 由
![](https://img.yulucn.com/upload/f/e9/fe9b99692e28a6a20e8a3fbaab3549e2_thumb.jpg)
可得
∴
![](https://img.yulucn.com/upload/1/ec/1ecae08517ce1d671659926b8c3146fd_thumb.jpg)
, 9分
令
![](https://img.yulucn.com/upload/e/6e/e6ea69c0314bb52a6bf3a872aee88059_thumb.jpg)
,则
![](https://img.yulucn.com/upload/4/00/40004d47e1cd4dc4f8437a290a3d9dbe_thumb.jpg)
10分
1年前
8